Industrialization of Electropolishing (EP)D.Proch, DESY

• EP is the preferred cleaning method for superconducting Nb resonators (besides Buffered Chemical Polishing, BCP)

• There are experimental type EP installations in several laboratories

• Worldwide there was only one industrial EP facility at Japan (Nomura plating)

• EP activities in CARE:– Optimize EP parameters (DESY, Saclay, INFN

Legnaro)– Transfer EP technology to industry– Develop quality assurance methods (QA) for EP

Electro-chemistry of EP• Oxidation

2 Nb + 5 SO4-- + 5 H2O Nb2 O5 + 10 H+ + 5 SO4-- + 10 e-

• ReductionNb2 O5 + 6 HF H2 NbOF5 + Nb O2 F 0.5 H2 O +

1.5 H2 O

Nb O2 F 0.5 H2 O + 4 HF H2 Nb O F5 + 1.5 H2 O

• Important:– HF is a very toxic acid!!!– Hydrogen gas is produced

Principle arrangement of EP

New EP electrode at DESY EP

Al cathodeAcid injection holeon top of the cavity equator

Teflon insulator covering the electrode in the beam tube area

PE spacer holding the TEFLON Nitrogen overlay tube

PTFE net covering the electrodes

Details of the EP mechanical frame

Timing belt disc

Disks for sliding current transmitter

Current leads

Cathode feed trough at the beam pipe flange

current leads

alumina electrode

Nitrogen overlay inlet pipe

disc for sliding current transmitter

Gas outlet towards exhaust cleaner ( nitrogen, hydrogen and evaporated HF)

EP installation at DESY

EP Installation at Henkel,1

EP installation at Henkel,2

EP installation at ACCEL

Best candidates for EP electrolyte quality assurance (Henkel Study)

• Titration• ICP-OES (inductively coupled plasma-

optical emission spectroscopy)• IC (ionic-chromatography)• TOC (total organic carbon)• NMR (nuclear magnetic resonance)• FTIR-ATR-probe (Fourier transformation

infrared spectroscopy –attenuated total reflection)

Method Applicability

Titration total acidity

ICP-OES all elements (Nb, Fe,..)

IC + distillation Ions (So4, F-, FSO3H

TOC organic impurities

NMR organic impurities

FTIR-ATR-probetotal overview of components defined by the ATR data base

Overview QA methods for EP electrolyte (Henkel study)

Summary EP industrialization,1

• The goal of this task was to explore and optimize the important operating parameters of the DESY EP system and to transfer this technology to industry.

• At DESY 176 EP treatments of 9-cell cavities have been carried out

• The EP technology has been successfully transferred to industry.

• Two companies (ACCEL and Henkel) have designed, built, installed and operated EP installations based on the experience with electropolishing at DESY.

Summary EP industrialization,2

• Up to now ACCEL and Henkel have treated 24 cavities in total

• In addition a QA strategy for the EP electrolyte has been worked out by Henkel company

• Electropolishing infrastructure & expertise at two companies is available now in Europe for EP cleaning of TTF type multi-cell Nb resonators

Hazard of HFRepair of a leak in the heat exchanger